Source Stocks

This gene is very difficult to identify with certainty because pathogen isolates avirulent for Sr18 usually possess additional genes for avirulence which render them unable to attack most wheat cultivars. Nevertheless, workers at The University of Sydney demonstrated its presence in most wheats (Baker et al., 1970). Indeed McIntosh (1988a) considered it more convenient to list wheats not possessing Sr18. These included Chinese Spring (Loegering and Harmon, 1969); Eureka (Baker et al., 1970); Federation (Baker et al., 1970); Little Club (Loegering and Harmon, 1969); Morocco (Baker et al., 1970); Prelude (Loegering and Harmon, 1969) and Yalta (Baker et al., 1970) as well as W2691 and Line E, both of which were especially bred at The University of Sydney for susceptibility to pathogen cultures with unusual genes for avirulence, including P18. The presence of p18 in P. graminis f. sp. tritici would be essential because Sr18 occurs in most common wheats. In contrast, P18 is unnecessary in P. graminis f. sp. secalis due to the absence of Sr18 in cereal rye. In this way genes such as Sr18 play a role in host specialisation.

Seedling leaves of (L to R): IHope 1D-Ra, W2691 /Purple Straw Selection, and tine AD = W2691*5/Kota; infected with University of Missouri culture 111 x 36.#97. The first two wheats show the reaction typical of plants with Sr18 whereas the high resistance of the third plant is conferred by Sr28.